JPH1174727A - Voltage controlled oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the voltage controlled oscillator with a small size whose C/N characteristic is enhanced. SOLUTION: A resonance circuit 11 is provided with a capacitor C1, a varactor diode VD, and a resonator S consisting of a strip line whose one end connects to ground. An oscillation circuit 12 is provided with an oscillation transistor(TR) Q1, bias resistors R1, R2, R3, Colpitts capacitors C4, C5, a high frequency bypass capacitor C6, and a chip capacitor Cc whose one end connects in series with the bias receiver R3 and whose other end connects to ground. Then a connection part between the bias resistor R3 and the chip capacitor Cc of the oscillation circuit 12 is connected to the resonator S consisting of the slip line in the resonance circuit 11 via a connection line L, then an emitter of the oscillation TR Q1 of the oscillation circuit 12 connects to ground via the bias resistor R3 and the resonator S, then the resonator S and the chip capacitor Cc configure a parallel resonance circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled oscillator for controlling the frequency of an output signal by an input voltage value, and more particularly to a voltage controlled oscillator having improved C / N characteristics.

[0002]

2. Description of the Related Art A conventional voltage controlled oscillator for improving C / N characteristics is disclosed in Japanese Patent Application Laid-Open No. 8-148933.
There is one disclosed in Japanese Patent Application Laid-Open Publication No. HEI 9-125, which will be described with reference to FIG.

A voltage controlled oscillator is, for example, 900 MHz
A resonance circuit 1 used in a z-band mobile communication device and having a control terminal C, an output terminal P, and a resonance frequency that varies according to a control voltage Vc applied to the control terminal C; An oscillation circuit 2 whose oscillation frequency is determined by one resonance frequency; and a buffer for amplifying a signal output from the oscillation circuit 2 and preventing the oscillation frequency of the oscillation circuit 2 from fluctuating due to load fluctuation. The circuit 3 includes an output matching circuit 4 for matching a circuit 3 and an external circuit (not shown) connected to the output terminal P and for suppressing harmonics. Each circuit of such a voltage controlled oscillator includes, for example, a plurality of electronic component functions to be described later on and inside a multilayer circuit board obtained by stacking and simultaneously firing a plurality of ceramic sheets on which circuit patterns are printed. Is formed.

The resonance circuit 1 includes a coupling capacitor C
1, a variable capacitance diode VD, and a resonance inductor L
1 and a resonance capacitor C2. The control voltage Vc applied to the control terminal C is
2 to the variable capacitance diode VD. In addition. The control terminal C is high-frequency grounded by a high-frequency bypass capacitor C3.

The oscillation circuit 2 includes an oscillation transistor Q1 as an active element, bias resistors R1, R2, R3,
Colpitts capacitors C4 and C5, a high-frequency bypass capacitor C6, a strip line SL connected in series to the bias resistor R3, and a chip capacitor Cc connected in parallel to the strip line SL. Form a parallel resonance circuit. The oscillation circuit 2 includes a coupling capacitor C7
Is connected to the resonance circuit 1 via the. Further, the bias resistor R3 defines a DC bias of an emitter as a current output terminal of the oscillation transistor Q1.

The buffer circuit 3 includes a buffer transistor Q2 and bias resistors R4 and R5. The buffer circuit 3 is connected to the oscillation circuit 2 via a coupling capacitor C8.

The output matching circuit 4 includes a choke coil L3
, A coupling capacitor C10, a high-frequency bypass capacitor C11, and an output terminal P.

A driving power supply terminal B for applying a driving power supply VB to the oscillation transistor Q1 and the buffer transistor Q2 is connected to a high-frequency bypass capacitor C1.
2 is grounded at a high frequency.

Then, by changing the capacitance value of the variable capacitance diode VD constituting the resonance circuit 1 according to the value of the control voltage Vc, the resonance frequency of the resonance circuit 1 changes, and the oscillation circuit changes at the resonance frequency. 2 oscillates, and its output signal is output from the output terminal P.

By the way, the quality factor Q of the resonance circuit 1 is most affected by the impedance of the emitter of the oscillation transistor Q1 serving as the load of the resonance circuit 1, and the higher the impedance of the emitter, the less the Q of the resonance circuit 1 deteriorates.
The C / N characteristics of the voltage controlled oscillator are improved.

In the voltage controlled oscillator configured as described above, the strip line SL and the chip capacitor C
c, by changing the inductance value of the strip line SL and the capacitance value of the chip capacitor Cc individually, so that the resonance frequency between the strip line SL and the chip capacitor Cc matches a predetermined frequency. The C / N characteristic of the voltage controlled oscillator is improved by increasing the impedance of the emitter of the oscillation transistor Q1 at a predetermined frequency.

[0012]

However, in the above-mentioned conventional voltage controlled oscillator, the resonance inductor L1 of the resonance circuit 1 is generally constituted by a strip line resonator. Therefore, two strip lines, a strip line resonator as the resonance inductor L1 and a strip line SL of the oscillation circuit 2, exist in the voltage controlled oscillator.

These strip lines are formed as circuit patterns on a multilayer circuit board, and both strip lines require a certain length as a strip line in order to obtain sufficient characteristics. However, in order to ensure a sufficient length of the strip line, it is necessary to increase the size of the multilayer circuit board, and accordingly, the voltage-controlled oscillator itself becomes large. It was difficult.

Further, since the strip line resonator and the strip line L1 exist in one multilayer circuit board constituting the voltage controlled oscillator, electrical coupling between the strip lines occurs, and as a result, the Q of the resonance system is reduced. The C / N characteristics were degraded.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide a voltage controlled oscillator which can improve the C / N characteristics and can be downsized.

[0016]

In order to achieve the above object, a voltage controlled oscillator according to the present invention comprises: a resonance circuit having a resonator constituted by a strip line or a microstrip line and having one end grounded; And a oscillation circuit having an active element, wherein the active element is grounded via a resonator.

The active element is composed of a transistor, one end of a bias resistor for defining a DC bias of a current output terminal of the transistor is connected to the emitter of the transistor, and one end of a capacitor is connected to the other end of the bias resistor. When the other end of the capacitor is grounded, the emitter of the transistor is grounded via the bias resistor and the capacitor, and the connection between the bias resistor and the capacitor is connected to the resonator.
The transistor is characterized in that the emitter is grounded via a resonator.

Further, the active element is composed of a transistor, one end of a bias resistor for defining a DC bias of a current output terminal of the transistor is connected to the emitter of the transistor, and the other end of the bias resistor is connected to the resonator. Thereby, the emitter of the transistor is grounded via the resonator.

Thus, the number of strip lines is reduced because the strip lines as resonators also function as the strip lines provided in the emitter of the transistor in the conventional voltage controlled oscillator.

Further, a parallel resonance circuit is formed by the resonator and the capacitor. By changing the inductance value of the strip line and the capacitance value of the capacitor, C is reduced.
/ N characteristics can be improved.

Further, by increasing the impedance of the emitter of the transistor by changing the inductance value of the strip line, the C / N characteristics are improved without using a capacitor which has been conventionally required, and the number of parts is reduced. .

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a voltage controlled oscillator according to a first embodiment of the present invention. The same components as those of the conventional voltage controlled oscillator shown in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted.

This voltage controlled oscillator differs from the conventional voltage controlled oscillator in the configuration of the resonance circuit and the oscillation circuit. Therefore, these circuits will be described.

The resonance circuit 11 includes a coupling capacitor C1, a variable capacitance diode VD, and a resonator S composed of a strip line. Here, one end of the resonator S is grounded. The control voltage Vc applied to the control terminal C is given to the variable capacitance diode VD via the choke coil L2. In addition. Control terminal C
Are grounded at a high frequency by a high-frequency bypass capacitor C3.

The oscillation circuit 12 includes an oscillation transistor Q1 as an active element and bias resistors R1, R2, R3
, Colpitts capacitors C4 and C5, a high-frequency bypass capacitor C6, and a chip capacitor Cc having one end connected in series to the bias resistor R3 and the other end grounded.
The oscillation circuit 12 is connected to the resonance circuit 11 via the coupling capacitor C7. Also, the bias resistor R
Reference numeral 3 defines a DC bias of the emitter as a current output terminal of the oscillation transistor Q1. The emitter of the oscillating transistor Q1 is grounded via a series circuit including a bias resistor R3 and a chip capacitor Cc.

The bias resistor R3 of the oscillation circuit 12
Is connected to the resonator S composed of a strip line in the resonance circuit 11 via the connection line L, so that the emitter of the oscillation transistor Q1 of the oscillation circuit 12 is connected to the bias resistor R3. And resonator S
, And a parallel resonance circuit is formed by the resonator S and the chip capacitor Cc.

In the voltage controlled oscillator configured as described above, the resonator S composed of a strip line also functions as a strip line connected to the emitter of the oscillation transistor Q1. The parallel resonance circuit composed of the resonator S and the chip capacitor Cc is connected to a strip line so as to be AC-opened in a frequency band where the voltage controlled oscillator is used, for example, in a 900 MHz band in the embodiment of the present invention. The length and the capacitance value of the chip capacitor Cc are determined in advance. That is, by individually changing the inductance of the resonator S composed of the strip line of the oscillation circuit 12 and the capacitance of the chip capacitor Cc, the resonance frequency of the parallel resonant circuit composed of the strip line and the chip capacitor Cc is increased by 900.
The C / N characteristic of the voltage controlled oscillator is improved by increasing the impedance of the emitter of the oscillation transistor Q1 in the 900 MHz band so as to match the MHz band.

The voltage controlled oscillator configured as above is
Since the number of strip lines is reduced as compared with the conventional voltage controlled oscillator, the circuit is simplified, and the size of the voltage controlled oscillator is reduced. That is, in the multilayer circuit board (not shown) constituting the voltage controlled oscillator, the wiring pattern in the multilayer circuit board for one strip line can be simplified, so that the board area can be reduced as compared with the related art. Becomes

The length of the strip line functioning as a parallel resonance circuit is determined by the bias resistor R3 and the chip capacitor C.
The connection line L, which is drawn from the connection portion with the capacitor c, is determined by the position where the connection line L is connected to the resonator S composed of a strip line. It is determined by the capacitance value of Cc. When a sufficient impedance can be obtained only by the strip line, as shown in FIG. 2, the chip capacitor Cc can be eliminated, the circuit constituting the voltage controlled oscillator is further simplified, and the size of the voltage controlled oscillator can be reduced. Is achieved.

In the above-described embodiment, the case where the resonator S is formed of a strip line has been described. However, the resonator S may be formed of a microstrip line, and the same effect is obtained in that case. Needless to say.

In the above-described embodiment, the oscillation transistor Q1 is used as an active element. However, the present invention is not limited to the transistor. For example, an FET may be used. You can do it.

[0032]

As described above, in the voltage controlled oscillator according to the present invention, the strip line as the resonator also functions as the strip line connected to the emitter of the oscillation transistor provided in the conventional voltage controlled oscillator. Therefore, the number of strip lines is reduced, the substrate area is reduced, and the size of the voltage controlled oscillator is reduced.

Further, a parallel resonance circuit is formed by the resonator and the capacitor. By changing the inductance of the strip line and the capacitance of the capacitor, C / C
N characteristics can be improved.

Further, by increasing the impedance of the emitter of the transistor by changing the inductance of the strip line, it is possible to improve the C / N characteristics without using a conventionally required capacitor and to reduce the number of parts. Because of the reduction, the cost can be reduced, and the circuit is simplified and the voltage-controlled oscillator can be downsized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a voltage controlled oscillator according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a voltage controlled oscillator according to another embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of a conventional voltage controlled oscillator.

[Explanation of symbols]

 Reference Signs List 11 resonance circuit 12 oscillation circuit Q1 oscillation transistor R3 bias resistor S resonator Cc chip capacitor

Claims (3)

[Claims] 1. A resonance circuit having a resonator constituted by a strip line or a microstrip line and having one end grounded; an oscillation circuit having an active element for oscillation;
The voltage controlled oscillator according to claim 1, wherein the active element is grounded via the resonator. 2. The method according to claim 1, wherein the active element comprises a transistor, one end of a bias resistor for defining a DC bias of a current output terminal of the transistor connected to an emitter of the transistor, and a capacitor connected to the other end of the bias resistor. Is connected to the other end of the capacitor, and the other end of the capacitor is grounded, so that the emitter of the transistor is grounded via the bias resistor and the capacitor, and the connection between the bias resistor and the capacitor is connected to the resonance. 2. The voltage controlled oscillator according to claim 1, wherein the emitter of the transistor is grounded via the resonator by being connected to a resonator. 3. The transistor according to claim 1, wherein the active element includes a transistor, one end of a bias resistor that defines a DC bias of a current output terminal of the transistor is connected to an emitter of the transistor, and the other end of the bias resistor is connected to the resonance terminal. 2. The voltage controlled oscillator according to claim 1, wherein the emitter of the transistor is grounded via the resonator by being connected to a resonator.